Choy JS, O'Toole E, Schuster BM, Crisp MJ, Karpova TS, McNally JG, Winey M, Gardner MK, Basrai MA

How subunit dosage contributes to the assembly and function of multimeric complexes is an important question with implications in understanding biochemical, evolutionary, and disease mechanisms. Toward identifying pathways that are susceptible to decreased gene dosage we performed a genome-wide screen for haploinsufficient (HI) genes that guard against genome instability in ...

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S. cerevisiae. This led to the identification of all three genes (SPC97, SPC98, and TUB4) encoding the evolutionarily conserved γ-TuSC that nucleates microtubule assembly. We found that hemizygous γ-TuSC mutants exhibit higher rates of chromosome loss and increases in anaphase spindle length and elongation velocities. Fluorescence microscopy, FRAP, electron tomography and model convolution simulation of spc98/+ mutants revealed improper regulation of interpolar (iMT) and kinetochore (kMT) microtubules in anaphase. The underlying cause is likely due to reduced levels of Tub4 as overexpression of TUB4 suppressed the spindle and chromosome segregation defects in spc98/+ mutants. We propose that γ-TuSC is crucial for balanced assembly between iMTs and kMTs for spindle organization and accurate chromosome segregation. Taken together this report shows how gene dosage studies provide critical insights into the assembly and function of multisubunit complexes that cannot be understood using traditional studies with haploid gene deletion or conditional alleles.

Date: Jul. 03, 2013

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